Bone plate

ABSTRACT

A bone plate has an underside on the side of the bone, an upper side and a plurality of holes in the plate connecting the underside with the upper side, with a central hole axis. At least one of these holes in the plate has an internal jacket surface that tapers towards the underside, while the internal jacket surface has N≧3 recesses which extend radially away from the axis of the hole.

RELATED APPLICATION DATA

The present application is a continuation of the U.S. National Stagedesignation of co-pending International Patent Application No.PCT/CH2003/000577, filed Aug. 26, 2003, the entire content of which isexpressly incorporated herein by reference thereto.

FIELD OF THE INVENTION

The invention relates to a bone plate for use in repairing bonefractures.

BACKGROUND OF THE INVENTION

Bone plates are known in the art and may be indicated for the entireskeleton. Particularly significant are, however, the usual large andsmall fragment indications for surgically treating bone breakages.

From DE-A 198 32 513 a bone plate of the generic type is known. In thecase of this known device, the angular alignment of the bone screwsrelative to the bone plate and their angularly stable fixing is achievedby a ring arranged between the head of the screw and the hole in theplate. A disadvantage of this construction is, on the one hand, the moreexpensive manufacture with an additional component (ring) and the dangerthat the tiny ring will fall out or be pushed out from the hole in theplate, thus making the device unusable, and, on the other hand, the moreexpensive OP technique because the axis of the ring has to becorrespondingly aligned before inserting the screw.

The present invention seeks to remedy this problem. The object of theinvention is to produce a bone plate, without the need for additionalcomponents, that can accommodate conventional locking capscrews in anangularly and axially stable manner.

SUMMARY OF THE INVENTION

The invention achieves this objective with a bone plate having an uppersurface, a lower surface, and at least one hole extending from the uppersurface to the lower surface, the at least one hole having a centralhole axis and an internal jacket surface. The internal jacket surfaceincludes N recesses extending radially away from the central axis, whereN≧3. The internal jacket surface may also include surface projections onat least a portion of the internal jacket surface.

The advantage achieved by the invention is essentially that as a resultof the bone plate according to the invention a bone screw can beintroduced at an angle that is different from the specified axis of thehole (usually at right angles to the plane of the bone plate) andsecured in this position, without significantly sacrificing thestability, as is the case in known devices.

By virtue of the at least three recesses in the internal jacket surfaceof the holes in the plate, centralizing bearing surfaces are producedfor the capscrew, even when the bone screw is inclined, and the bearingsurfaces result in an even distribution of the load. In the case of bonescrews with a threaded head and holes in the plate with an inner thread,when the screw is inclined, the threaded head can “jump over” thepitches of the thread in the hole of the plate interrupted by therecesses, without “cutting through” them.

A further advantage of the bone plate according to the invention is thepossibility to use the at least three recesses in the hole in the plateto guide drilling bushings or guide bushings, by which the bone screwscan be guided during their insertion. In this case the drilling bushingsor guide bushings no longer need to be screwed into the holes in theplate (as is the case in the state-of-the-art), but due to the recessesneed only to be inserted into the holes in the plate, resulting in asimple manner in the centre and direction of the axis of the hole. Allthat is required for this purpose is that the tips of the cannulateddrilling bushings or guide bushings need to have the negative geometryof the holes in the plate, without any thread or other, similarlyacting, structures. A snap-in mechanism may possibly be used inconjunction.

In one particular embodiment, the internal jacket surface of the hole inthe plate is provided with a three-dimensional structure, which servesthe purpose of guiding of a correspondingly structured capscrew. Thethree-dimensional structure is macroscopic and preferably comprisespartial or complete pitches of a thread, ribs or protuberations. Theinternal jacket surface may be a multi-start thread.

The geometry of the surface of the N “locking leg”, formed by the Nrecesses, is advantageously constructed to facilitate compatibility withthe bone screw to be introduced. This can be in the form of a classichelical thread, a thread-like shape with or without pitch or also only acertain number of grooves or ribs, or also a quasi-thread with orwithout pitch. The number of grooves or ribs is preferably always odd(e.g. 3, 5, 7 or 9).

The internal jacket surface can have a concave, preferably spherical,tapered or ellipsoidal shape. This shape facilitates the insertion of abone screw in such a manner that at the first contact of the bone screwwith the internal jacket surface the bone screw is automatically pulledinto the hole in the plate, without exerting prior a compression forceon the bone via the bone plate, as is partly the case with devices knownin the art.

In the case of a further development, at least one of the holes in theplate is constructed as an oblong hole.

The N recesses are arranged at a distance of 360°/N relative to thecentral axis. The recesses preferably have a peripheral expansion of atleast 1° and a maximum of 119°. At the same time the N recesses dividethe internal jacket surface into N sections of the jacket surface.

In the case of a particular embodiment the recesses extend exclusivelywithin the internal jacket surface. In the case of another embodiment,the recesses extend radially away from the axis of the hole past theinternal jacket surface.

The recesses may extend cylindrically or tapered from the upper side tothe underside. The advantage of this is, that the recesses can be usedfor the fixing of a drilling bushing for pre-drilling or for theinsertion of the Kirschner wires. Thus the drilling bushing no longerhas to be screwed into the hole in the plate, only to be insertedwithout damaging the bearing area for the screw.

The recesses can extend from the upper side to the underside over theentire height of the bone plate.

The bone plate can be made from steel or titanium or also from a plasticmaterial. In the case of plastic plates from polyacryl etherketone(PEAK) or polyether etherketone (PEEK) with an elongation at break of40-70% and a modulus of elasticity of 3000-6000 N/mm² are preferred.However, polysulphon, having an elongation at break of 80-120% and amodulus of elasticity of 2000-3500 N/mm² may also be used. Furthermore,liquid crystal polymer (LCP) having an elongation at break of 1.5-2.5%and a modulus of elasticity of 5000-20000 N/mm² may be suitable.Finally, polyoxymethylene (POM) with an elongation at break of 10-50%and a modulus of elasticity of 2000-3500 N/mm² and polyphenylenesulphide (PPS) having an elongation at break of 0.2-1.0% and a modulusof elasticity of 12000-20000 N/mm² may be used.

Bone plates from plastic material may be reinforced with metal, plasticor carbon fibres.

Various bone screws can be used with the bone plates. For example, thosehaving a convex, preferably spherical or tapered head portion. The headportion of the bone screws may also have a three-dimensional structure.In the case of a special embodiment the head portion of the bone screwis made from a material that is harder than the internal jacket surfaceof the bone plate. The internal jacket surface of the bone plate and thehead portion of the bone screw have preferably matching threads.

In the case of a plastic plate, the holes in the plate may be executedas metallic thread inserts. Conversely, in the case of a metal boneplate the holes in the plate are executed as polymer thread inserts.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and developments of the invention are explained in detailbased on the partly schematic illustrations of several embodiments inthe figures, wherein:

FIG. 1 shows a longitudinal section through a bone plate with taperedholes in the plate;

FIG. 2 shows a longitudinal section through a bone plate with sphericalholes in the plate;

FIG. 3 shows a top view of a bone plate with three recesses in theinternal jacket surface of the holes in the plate;

FIG. 4 shows a variation of the bone plate according to FIG. 3 withlarger recesses in the internal jacket surface of the holes in theplate;

FIG. 5 shows a top view of a bone plate with thread inserts with fourrecesses in the internal jacket surface of the elliptic holes in theplate;

FIG. 6 shows a perspective view of a bone plate according to FIG. 1 fromabove with the bone screws inserted;

FIG. 7 shows a perspective view of a bone plate according to FIG. 1 frombelow with the bone screws inserted;

FIG. 8 shows a longitudinal section through a bone plate with a bonescrew inserted without angular misalignment; and

FIG. 9 shows a longitudinal section through a bone plate with a bonescrew inserted with angular misalignment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The bone plate 1 illustrated in FIGS. 1 and 3 has an underside 2 on theside of the bone, an upper side 8 and a plurality of holes 3 in theplate connecting the underside 2 with the upper side 8, the holes havinga central hole axis 5. The holes 3 in the plate have an internal jacketsurface 4 that tapers towards the underside 2. Furthermore, the internaljacket surface 4 has three recesses 6 which extend radially away fromthe hole axis 5 of the hole at a uniform distance of 120° from oneanother. Their peripheral extension is approximately 40° and they extendexclusively within the internal jacket surface 4. The recesses 6 extendtapered over the entire height of the bone plate 1 from the upper side 8to the underside 2. In addition, the internal jacket surface 4 isprovided with a three-dimensional structure 7 in the form of a thread.

FIG. 4 illustrates a variation of the execution according to FIG. 3,wherein the recesses extend radially away from the axis of the hole pastthe internal jacket surface.

FIGS. 2 and 5 illustrate a further alternative embodiment, wherein theholes 3 in the plate are constructed as oblong holes. The bone plate ismade basically from a plastic material (PEEK) with embedded metallicthread inserts 9 from titanium, forming the holes 3 in the plate. In thecase of this embodiment the holes 3 in the plate have four recesses 6,which extend radially away from the axis 5 of the hole past the internaljacket surface 4. The internal jacket surface 4 is divided into foursections of the jacket surface. The recesses extend tapered over theentire height of the bone plate 1 from the upper side 8 to the underside2. In addition, the internal jacket surface 4 is provided with athree-dimensional structure 7 in the form of a multi-start thread. Asfar as material is concerned, this embodiment may also be inverted,whereby the bone plate is basically made from metal (titanium) and theembedded therein thread inserts 9 are made from plastic material (PEEK),forming the holes 3 in the plate.

FIG. 6 illustrates the bone plate according to FIG. 1, with bone screws10 inserted from above, the head portions 11 of which are spherical.FIG. 7 shows the same bone plate 1 from below.

In FIG. 8, a bone plate 1 is illustrated with bone screws 10 insertedtherein without angular misalignment. The internal jacket surface 4 ofthe hole of the bone plate 1 and the head portion 11 of the bone screw10 have matching threads 13.

FIG. 9 illustrates the same variation as FIG. 8, while the bone screw 10is angularly misaligned.

While the present invention has been described with reference to thepreferred embodiments, those skilled in the art will recognize thatnumerous variations and modifications may be made without departing fromthe scope of the present invention. Accordingly, it should be clearlyunderstood that the embodiments of the invention described above are notintended as limitations on the scope of the invention, which is definedonly by the following claims.

1. A bone plate comprising: an upper surface; a lower surface; and atleast one hole extending from the upper surface to the lower surface,the at least one hole having a central hole axis and an internal jacketsurface, wherein the internal jacket surface includes N recessesextending radially away from the central axis, where N≧3 and theinternal jacket surface includes surface projections on at least aportion of the internal jacket surface.
 2. The bone plate of claim 1,wherein the internal jacket surface tapers towards the lower surface ofthe plate.
 3. The bone plate of claim 1, wherein the internal jacketsurface has a concave shape.
 4. The bone plate of claim 1, wherein theinternal jacket surface has a spherical or ellipsoidal shape.
 5. Thebone plate of claim 1, wherein the hole is oblong in shape.
 6. The boneplate of claim 1, wherein the surface projections are threads or ribs.7. The bone plate of claim 1, wherein the N recesses are angularlyspaced at a distance of 360°/N relative to the central axis of the hole.8. The bone plate of claim 1, wherein each recess has a peripheralexpansion of at least 1°.
 9. The bone plate of claim 1, wherein eachrecess has a maximum peripheral expansion of 119°.
 10. The bone plate ofclaim 1, wherein the recesses extend exclusively within the internaljacket surface of the hole.
 11. The bone plate of claim 1, wherein therecesses extend radially away from the axis of the hole beyond theinternal jacket surface.
 12. The bone plate of claim 1, wherein theupper surface and lower surface of the plate define a plate thickness,and the recesses extend from the upper surface to the lower surface overthe entire thickness of the bone plate.
 13. The bone plate of claim 1,wherein the surface projections on the internal jacket surface of thehole are formed in a direction substantially perpendicular to thecentral axis of the hole.
 14. The bone plate of claim 1, wherein theplate is formed of polyacryl etherketone (PEAK) or polyether etherketone(PEEK) with an elongation at break of 40-70% and a modulus of elasticityof 3000-6000 N/mm².
 15. The bone plate of claim 1, wherein the plate isformed of polysulphon with an elongation at break of 80-120% and amodulus of elasticity of 2000-3500 N/mm².
 16. The bone plate of claim 1,wherein the plate is formed of liquid crystal polymer (LCP) with anelongation at break of 1.5-2.5% and a modulus of elasticity of5000-20000 N/mm².
 17. The bone plate of claim 1, wherein the plate isformed of polyoxymethylene (POM) with an elongation at break of 10-50%and a modulus of elasticity of 2000-3500 N/mm².
 18. The bone plate ofclaim 1, wherein the plate is formed of polyphenylene sulphide (PPS)with an elongation at break of 0.2-1.0% and a modulus of elasticity of12000-20000 N/mm².
 19. The bone plate of claim 1, wherein the plate isformed of a metal, plastic or carbon fibre reinforced plastic material.20. The bone plate of claim 1, further comprising at least one bonescrew having a tapered head portion configured and adapted to interfacewith the surface projections on the internal jacket surface of the holefor angularly stable anchoring in the plate.
 21. The bone plate of claim20, wherein the internal jacket surface and the head portion of the bonescrew have matching threaded surfaces.
 22. A bone plate comprising: anupper surface; a lower surface; a plate thickness defined by the upperand lower surfaces; at least one hole extending from the upper surfaceto the lower surface, the at least one hole having a central hole axis,a periphery, and an internal surface; a plurality of surface projectionson the internal surface of the hole, the projections oriented generallyperpendicular to the central axis of the hole; and at least threerecesses in the internal surface of the hole angularly spaced about theperiphery and extending radially away from the central axis wherein therecesses extend from the upper surface to the lower surface over theentire thickness of the bone plate.
 23. The bone plate of claim 22,wherein the internal surface of the hole tapers towards the lowersurface of the plate.
 24. The bone plate of claim 23, further comprisingat least one bone screw having a tapered head portion configured andadapted to interface with the surface projections on the internalsurface of the hole for angularly stable anchoring in the plate.
 25. Thebone plate of claim 22, wherein each recess angularly extends at least40° along the periphery of the hole about the central axis.